This invention relates to a continuous process for the manufacture of fiber-reinforced or other reinforced webs of heat-curable plastics, which may be bonded to further plies, such as base films, decorative films or covering films, and to an apparatus for carrying out the process.
Processes for the continuous manufacture of webs of heat-curable resins, such as, for example, epoxy resins or polyester resins, which are fiber-reinforced or reinforced in some other way by insertion of porous materials, are known, and in these the transportation of the laminate during manufacture can be effected by an endless, circulating conveyor belt [P. Selden, Glasfaserverstaarkte Kunststoffe (Glass Fiber-Reinforced Plastics), Springer Verlag 1967, page 558]. In such processes, continuous curing mostly has been effected by heating in a long heating zone, see, for example, P. Selden, page 612; this heating zone also may be a heated belt press (Austrian Patent Specification No. 349,366).
The impregnation of the reinforcing insert, preferably a fiber mat or inserted individual filaments, with the resin is in most cases effected by the so-called dipping process, by passage through an impregnating trough (Austrian Patent Specification No. 349,366), the excess resin subsequently being removed either by means of a calibrating slit (Austrian Patent Specification No. 349,366) or by squeeze-off rollers (see E. W. Laue, Glasfaserverstarkte Polyester und andere Duromere (Glass Fiber-Reinforced Polyesters and Other Thermosetting Resins), Zechner & Huthig Verlag GmbH, Speyer-Vienna-Zurich, page 332). These methods of resin removal lead, especially where high glass contents are employed, to fiber breakages which detract from the strength of the laminate.
It has also been proposed to apply the resin, where a continuous process is involved, by means of a doctor device (see P. Selden, pages 611 and 612).
In all these processes, care must be taken that the resin is applied uniformly and that wetting and impregnation of the fiber material is achieved without formation of air bubbles. This becomes more difficult as the glass content is increased, and in all processes a difficulty encountered is that the air introduced is released only slowly or only incompletely from the resin, sometimes being hindered from free release by items of the apparatus.